dt-bindings: iio: adc: Add docs for LTC2499

Update the bindings documentation for ltc2497 to include the ltc2499.

Signed-off-by: Ciprian Regus <ciprian.regus@analog.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220916140922.2506248-3-ciprian.regus@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>